The present invention relates to a copier, image reader, facsimile transceiver or similar image recorder and, more particularly, to a device incorporated in an image recorder for sensing the size of a document laid on a glass platen to be copied.
An image recorder of the type laying a document to be copied on a glass platen, scanning the document to read an image thereof, and then reproducing it on a paper or similar recording medium is conventional. It is a common practice with this type of image recorder to determine the size of the document positioned on the glass platen in the event of reading an image printed on the document. For this purpose, it has been customary to arrange a group of sensors responsive to the document width below the glass platen in a main scanning direction, and another group of sensors responsive to the document length in the subscanning direction. Such a sensing device, however, cannot cope with many document sizes without resorting to a great number of sensors in each of the main and subscanning directions. Moreover, since each sensor is made up of a light emitting element and a light-sensitive element, a great number of optical elements are required in total, increasing the cost of the sensing device.